To be sente, in Japanese, means to have the initiative. This is a key concept of strategic games like Go. It can also be understood as doing something new before the others, or doing important things first, instead of urgent things later.
The word is split in its two syllables, or Japanese words, to help readers guess the correct pronunciation (“sentay”). The colon, made of Go stones, is a reminder of the syntax of messages in Smalltalk and Objective C, elegant and advanced computer languages.